1. Field of the Invention
This invention relates to a focal plane shutter for digital cameras.
2. Description of Related Art
Focal plane shutters for digital cameras includes a plane focal shutter which is provided with two shutter blades, a front blade and a rear blade. And, this type of focal plane shutter is usually formed in such a way that: the front and rear blades are connected to driving members for the front and rear blades respectively; in the set state in which shooting is not performed, the front blade covers an exposure aperture and the rear blade draws apart from the exposure aperture; and in shooting, these two driving members are rotated in turn and in the same direction by biasing forces of driving springs for the front and rear blades respectively so that the front blade opens the exposure aperture and the rear blade is closed after the opening of the exposure aperture in order to expose the imaging plane of an image pick-up apparatus, like focal plane shutters for film-based cameras. Accordingly, digital cameras which are provided with focal plane shutters having such a constitution are provided with optical finders.
Also, in focal plane shutters for digital cameras having such a constitution, when the rear blade completely closes the exposure aperture, imaging information is sent from the image pick-up apparatus through an information processing circuit and is written to a memory device, and then a set operation is immediately performed. The set operation is performed in such a way that a set member which is rotated from its initial position makes the two driving members reverse up to the set state against the biasing forces of the driving springs for the two driving members respectively. And, it is known that constitutions for keeping the two driving members in their set states until next shooting is performed include constitutions which are called a locking-type constitution and a direct-type constitution respectively.
That is to say, the locking-type constitution is such that the two driving members are locked into locking members until the front and rear blades are made to perform the exposure operation in shooting. Accordingly, the set member can be formed in such a way that the set member returns to its initial position immediately after the two driving members are locked into the locking members at their set states respectively because of the set operation. However, the set member can also be formed in such a way that the set member is returned to its initial position prior to the operation of the front blade opening in releasing the camera shutter. And, two release members which can be actuated in turn by electromagnets respectively release the driving members which are locked into the locking members respectively, so that the exposure operations of the front and rear blades are performed.
On the other hand, the direct-type constitution is such that: each of the two driving members is provided with an iron piece member; and the set member rotates the two driving members against the biasing forces of the driving springs for the two driving members until the iron-piece members come into contact with electromagnets which are not excited yet, because of the set operation. Accordingly, the set member is formed in such a way that: the set member is not made to return to its initial position immediately; the set member is kept in a state of the set member making the iron-pieces members come into contact the electromagnets also after that; and the set member is returned to its initial position after each of the electromagnets is excited and the electromagnets attract and hold the iron-piece members through their magnetic attraction forces in a release of the camera. And then, the electromagnets are demagnetized in turn in order to release the magnetic attraction forces which act on the iron-piece members, so that the exposure operations of the front and rear blades are performed.
The present invention relates to a focal plane shutter for digital cameras having the locking-type constitution of the above-described constitutions. A focal plane shutter for cameras which has such a locking-type constitution and is available for both digital and film-based cameras is disclosed in Japanese Patent Kokai No. 2001-305605.
Now, also in a digital camera which is provided with such a focal plane shutter having the locking-type constitution, there is a demand that shooting can be performed with an electronic view monitor (which is called “monitor” hereinafter) having a display device like liquid crystal or EL (Electroluminescence) even in the case where the digital camera is provided with an optical view finder (which is called “optical finder” hereinafter), in recent years. And, in this case, it is preferred that an image sensor for shooting is also used for monitor. In recent years, while shooting which is performed with an optical finder is called normal shooting (optical view shooting), shooting which is performed with such a monitor has come to be called live-view shooting or the like, independently of whether a focal plane shutter has the locking-type construction or the direct-type constitution.
Also, a plurality of shooting modes for a focal plane shutter including two shutter blades are known in the case where shooting is performed with a monitor the image sensor of which is also used as an image sensor for shooting. Typical one of the shooting modes is performed in such a way that: both front and rear blades are made to drawn apart from an exposure aperture in the set state; and when a release button is pressed in shooting, the front blade is actuated so as to cover the exposure aperture in the first stage of the typical shooting mode, and both the front and rear blades are made to perform the exposure operation in turn in the next stage of the typical shooting stage. And, a locking-type focal plane shutter for digital cameras which makes it possible to perform such an operation is disclosed in Japanese Patent Kokai No. 2001-215555.
Also, among shooting modes except the above-described typical shooting mode into which the above typical shooting mode or a shooting mode with an optical finder can be changed by a photographer operating a selection means which is provided for a camera to perform shooting, there is a shooting mode in which: both front and rear blades are made to drawn apart from an exposure aperture; and when a release button is pressed in shooting, the front blade is not actuated and an image sensor is controlled by an electronic control circuit so as to start shooting, and the rear blade closes the exposure aperture so as to finish the shooting. In addition, there is also a shooting mode in which the electronic control circuit controls the operations in both of the start and termination of shooting without driving both the front and rear blades. Furthermore, a digital camera may be also formed in such a way that it is possible to shoot a moving image by operating the above selection means or pressing a second release button with both the front and rear blades made to draw apart from the exposure aperture so that the electronic control circuit repeatedly performs a set operation all the time the release button is pressed.